The invention refers to a multilayer material, consisting of a heat-activated substrate with a defined shrinkability on a polyester base, coated with a polymer and, if necessary, with a thermoplastic contact adhesive and, if necessary, coated with a layer for receiving toner or ink, or with a metallic coating.
Multilayer materials of this kind are suitable for covering large areas over a supporting framework in the construction of model aircraft and of one-man aircraft/ultralight aircraft. However, they are also suitable as a medium onto which images and print may be applied using a plain paper copier, and are used as weather-resistant, self-adhesive labels and marking materials and in advertising.
Because of their physical and chemical properties, coloured polyester films, made for example from polyethylene terephthalate are suitable for covering large areas on model aircraft, and are well known in this field. Due to their weather-resistant properties and resistance to heat, such films, when coated on one side with a layer for receiving toner or ink, can be used as a medium onto which images or print can be applied using a plain paper-copier.
Normal technical solutions involve coating transparent polyester substrates with a heat-activated, pigmented and/or coloured polymer adhesive layer. In addition there are polyester substrates in which a pigmented, thermoset polymer layer is bonded with the substrate by means of a thermoplastic polymer layer, with another thermoplastic polymer layer applied as an adhesive layer. Such films tend to be relatively heavy.
Fibrous supporting materials woven from polyester and impregnated with resin are also used in model aircraft construction to cover the wooden framework. The resinous solvents that are used can be coloured with pigments and/or organic colorants.
One disadvantage of these common technical solutions is, for example, the noticeable decline in the adhesive strength of those materials which are coloured by the application of pigmented adhesives. Moreover, the visual impact of, the covering material produced in this way depends largely on the conditions under which it is used and processed, thus making it impossible to guarantee consistent quality. Because of the thermoplasticity of such adhesives, when material is stretched over corners and edges cracks may occur in the pigment, with splits at the corners of the coloured/adhesive layer. Accidental contact with the adhesive layer and/or when adjustments are made to the covering material may spoil the continuity of the pigment structure.
Minute holes may be formed in the pigment layer of polyester films if their thermoset layer of pigment is embedded between two thermoplastic polymer layers, i.e. between the adhesive and its base. These are caused by a reaction in polyurethane systems between the hardener, such as isocyanate, and the thermoplastic adhesive layer. The reaction process releases gases (e.g. CO2, water), which then affect the pigment layer, forming minute holes.
Layers of toner are usually formed by applying bicyclical alkyl-, 1-12-C aliphatic alkyl or aromati-(meth)-acrylate with up to 20% of a polar monomer or N,N-dialkyl-mono-alkylamino-alkyl-(meth)-acrylate. Solutions of polymerised diol-di-(meth)-acrylate are also used, with additives consisting of copolymerised vinyl monomer and copolymerised vinyl ester, (meth)-acrylic esters and/or styrol. Transparent, aqueous layers that can accept toners and are made of water-soluble polymers, with polymer particles measuring between 1 and 15xcexc and with additives consisting of antistatic agents are also frequently used. Toner fixing layers are also used, made from polyvinylacetal resin with a degree of acetalisation of between 20-40 mol %. Furthermore, well known are water-soluble cellulose polymers containing non-ionic or ionic materials which are suitable for the production of transparent toner layers on polyester, e.g. Melinex or Hostaphan film.
And finally, clear polyester films with layers that can accept ink are also used, and are made up of vinyl, pyrrolidone particles of a polyester, a co-polymer of a 2-6-C alkylenoxide, a polyvinyl alcohol and inert particles. Current technology also means that viable films can also be made from polyethylene, polypropylene and polycarbonate, coated on one side to set the ink, and that this coating consists of emulsions/dispersions of vinyl chloride-vinyl acetate-copolymer resin. In general additives consisting of colloidal silicon oxide offer the best possible means of preventing the finished material from sticking.
A disadvantage of the films referred to above is that, depending on the type of application, and despite the fact that polyester films and non-woven materials are in principle suitable as the basic materials for weather-resistant coverings for model aircraft, and are resistant to tearing, such materials can only cover a limited area, and have a restrictive load-to-weight ratio. This means that they cannot be used for one-man aircraft.
Materials provided with the toner layers referred to above range from clear to opaque, and copies can be made in black on a transparent and/or opaque background. However, because of the transparency of the material they are of limited effectiveness or totally ineffective for advertising purposes.
The task of this invention is to improve the performance characteristics of heat-activated, coloured, shrinkable films on a polyethylene therephtalate base. Depending on the area of application of the film, in accordance with this invention, the film is polymer coated, firstly to enhance the surface finish of the thermoset pigmented film, to improve the tear-resistance of the film and to reduce the area weight, and secondly new areas of application are to be opened up by providing the film with a coloured backing, at the same time coating one side of the film with an impact adhesive. The purpose is also to coat the film in such a way that it can be used with copying systems.
A multilayer material and method of making same that overcomes the above disadvantages has now been discovered. In accordance with this invention, the multilayer material demonstrates improved performance characteristics with surprising effects when processed, as well as better resistance to tearing, and superior weather-resistance, compared with normal materials. In particular, as a result of so-called corona pre-treatment of the substrate, the film surface is modified in such a way (xe2x80x9croughenedxe2x80x9d) by chemical and physical methods that the bonding between the polymer coating and the substrate is substantially improved compared with normal methods. This is evident in the fact that the polymer coating is more effectively bonded to the film. However, this is subject to the precondition that the polymer coating process takes place immediately after the corona treatment.
The introduction of coloured pigments and/or fluorescent pigments and/or organic colorants to the reaction mixture, which consists of a hydroxy group polyurethane, preferably with hydroxyl groups in the final stage, and a low molecular weight linear polyisocyanate in a ratio of 20:1 with reference to solid polyurethane polymer, as the cross-linking agent, ensures a very homogenous coloration of the polymer layer. In accordance with this invention, a catalytic additive consisting of a tin-organic compound is used, reducing the polymerisation time to approximately 48 hours, compared with a period of several days if no catalyst is used.
The contact adhesive layer is applied using the well-known transfer method, in which contact adhesive materials are used on a polyacrylic basis in a commonly used composition. This is applied in solution to silicone paper, and after the solvent has evaporated it is bonded with the substrate under heat and pressure.
According to the invention, the side of the substrate opposite to the polymer coating is provided with a transparent reactive layer. This layer may be suitable for receiving toner or ink, and should preferably be of vinyl acetate, with the toner layer consisting of a substrate with a thickness of between 2 and 8 g/m.2 This creates a polymer film with a compact or translucent coloured backing, which can be used with a plain paper copier to accept images and printing, without adversely affecting the quality of the text and/or images thus reproduced. Such films are also ideal for advertising purposes because, as mentioned previously, the pigment is distributed homogeneously throughout the polymer layer, and they are also very weather-resistant due to the thermoset properties of the film.
In order to keep the so-called blocking effect on the toner or ink compatible layers to a minimum, if necessary between 0.5 and 5% of a suitable agent for preventing this effect is dispersed. Such agents may consist, for example, of colloid silicon dioxide or alternativelyxe2x80x94in the case of aqueous dispersionsxe2x80x94of up to a maximum of 3% rice starch. The reactive layer may be light-sensitive, thus opening up other possible uses.
Moreover, in accordance with the invention, it is intended that the side of the film opposite to the polymer coating should be provided with a thin metallic layer, i.e.  less than 1xcexc, made preferably of aluminium and/or chromium. This enables the area weight of the film to be substantially reduced. By applying the metallic layer to the coloured, transparent film the latter appears coloured but not translucent. Compared with existing methods for producing such coloured films, the system referred to in this invention can enable weight reductions of between 25 and 30% to be achieved, while the chemical and physical properties remain unchanged.
Another task is to find a process for producing the multilayer material. In accordance with the invention, these measures have resulted in a process that ensures that the multilayer material maintains a consistent quality. In accordance with the invention, if necessary, a reactive layer is applied to the side of the substrate opposite the polymer and contact adhesive coating, consisting, for example, of a layer suitable for taking toner or ink, and that, if necessary, an agent can be dispersed in this layer to avoid a blocking effect on the film. In accordance with the invention the film is fed past ionising rods in order to avoid or reduce the electrostatic charge that is built up on the substrate through friction against the rolls, causing the static on the substrate to be discharged again. An alternative is to apply a metallic layer using the vacuum vaporisation method.